there are a lot of thieves in amsterdam and generally coffee shop attendants are complete cocks. try to go to the zoo if you have the time
if the penniless attendant tries to hit you with the god act laugh at him, order 5 beers and tell him to bring it over to you, if he forgets the beer mats tell him to bring you beer mats. he's there to make the owner money! he knows that but you don't. if you happen to come across the owner (which you won't, but they'll insist they are) order some sandwichs. find a place that opens up on to the water, book a place to stay before you fly.
have a great time